A bomb calorimeter, or constant volume calorimeter, is a device often used to de

Question

A bomb calorimeter, or constant volume calorimeter, is a device often used to determine the heat of combustion of fuels and the energy content of foods. Since the "bomb" itself can absorb energy, a separate experiment is needed to determine the heat capacity of the calorimeter. This is known as calibrating the calorimeter. In the laboratory a student burns a 0.949-g sample of isophthalic acid (CgH04) in a bomb calorimeter containing 1140. g of water. The temperature increases from 24.70 °C to 27.90 °C. The heat capacity of water is 4.184 J goc The molar heat of combustion is 3203 kJ per mole of isophthalic acid CgH6O4(s) + 15/2 02(g)--8 CO2(g) +3 H2O(1) + Energy In Calculate the heat capacity of the calorimeter. heat capacity of calorimeter

Explanation / Answer

molar heat of combustion is the amount of heat released by the combustion of 1 mol of substance.

dH = dE + d nRT

dH = energy (heat) released at constant pressure

dH = energy released at constant volume.

n =no of moles of gas in product - no of moles of gas in reactant.

According to the Equation of combustion given in the queastion

dn = 8 - 15/16

= 0.5 mols

dH = -3203 KJ

dE = dH - dnRT

= -3203 - (0.5 * 8.314 * 298 ) (ideal gas equation applied)

= -3203 - ( 1238.7 ) converting dnrt value to KJ

= -3203 - 1.2

= 3204 KJ / mol

molecular mass of isopthalic acid = 166.14 g / mol

no of moles of isopthalic acid = 0.949 / 166.14

= 0.0057 mol

dE = q = C * dT, dE = q

enerergy released for 0.0057 mols

q = 0.0057 * 3204

= 18.26 KJ

Heat capacity c = q / dT dT = 27.9 - 24.7 = 3.20 C

c = 18.26 / 3.2

= 5.71 kJ / 0C

= 5710 J / 0C

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